1. Field of the Invention
The present invention relates to an apparatus for controlling the operation of a plurality of pilot-operated hydraulic devices provided in a working machine.
2. Description of the Related Art
As means for remotely controlling pilot-operated hydraulic devices provided in a working machine, there has been known an arrangement in which a pilot pressure input switching valve composed of an electromagnetic switching valve, etc. is provided between a pilot pressure input unit of the hydraulic devices and a pilot hydraulic pressure source, and the supply of the input signal of the pilot pressure to the pilot pressure input unit is switched by opening and closing the switching valve.
For example, Japanese Patent Laid-Open No. 2002-5106 discloses a hydraulic circuit in which a solenoid valve (electromagnetic switching valve) is provided between a pilot pressure input unit (swash plate) of a capacity variable hydraulic motor and a pilot hydraulic pump.
Also, Japanese Patent Laid-Open No. 2002-250302 discloses a circuit in which an electromagnetic switching valve is provided between a pilot-operated relief valve having a set pressure that increases with a pilot pressure input and a pilot hydraulic pressure source.
In the above-described hydraulic circuits, if there are a plurality of pilot-operated hydraulic devices, pilot pressure input switching valves are provided correspondingly for pilot pressure input units of the respective hydraulic devices. Therefore, the more the number of hydraulic devices, the more the number of pilot pressure input switching valves accompanying the devices, which increases the complexity and cost of the apparatus inevitably. Particularly, in the case of less frequently used hydraulic devices, the use of a pilot pressure input switching valve, if provided specially for the hydraulic devices, becomes far less frequent, being economically undesirable.